1. Field of the Invention
This invention relates generally to a technique for measuring the width of a noisy pulse in an analog signal and, more particularly, to a technique for remotely determining whether a valve associated with a cylinder in a locomotive diesel engine is defective by measuring the width of ultrasonic pulses emitted therefrom.
2. Discussion of the Related Art
Locomotives employ diesel engines having sixteen or more cylinders. Each cylinder employs several valves, for example four valves, where some of the valves allow a fuel/air mixture to be emitted into the cylinder and other of the valves allow exhaust gas to be removed from the cylinder. It is important that the seal integrity of the valve relative to the valve seat around the opening in the cylinder is sufficient so that the engine operates properly and is not damaged. However, the rigors of the combustion process within the cylinder sometimes causes cracks and other defects in the valve or the valve seat which may affect seal integrity. Continued operation of the engine with a defective valve may cause valve failure. Further, valve failure in a locomotive engine can result in damage to the engine turbocharger which may cost $100,000.00 or more to replace or fix.
Heretofore, it was usually necessary for a technician to visually inspect the valve and valve seat to look for evidence of cracking or other damage during maintenance over hauls and the like. This is a costly process because the valve head needs to be removed and each valve inspected which includes significant labor and downtime. Further, the inspection process is highly subjective in that the technician determines whether a defect exists by his or her own visual assessment and experience.
To overcome these problems, it is known in the art to employ a detection system including an ultrasonic sensor probe that detects ultrasonic emissions from the engine while it is idling. Ultrasonic emissions are typically emitted from the engine during such times as fuel injection and exhaust emission when the valves are opened. The probe is placed in contact with suitable locations on the cylinder head and a measurement is taken for each cylinder. The detection system includes processing circuitry that provides heterodyning by mixing the ultrasonic signal for frequency down-conversion purposes, for example 40 kHz to 0-3 kHz, to make the sound energy audible. The detection system also includes a headset for listening to the down-converted signal.
Because a defect in the valve causes additional gases to leak during the compression stroke, additional ultrasonic energy is emitted if such a defect exists. Therefore, by knowing the “sounds” that the engine cylinder makes with no defect, a technician can listen for higher intensity signals indicating the presence of a valve defect. However, such a technique for determining valve defects still includes a subjective aspect where the technician must determine the defect by the sound perceived. It would be desirable to provide a more cost effective and objective technique for determining if a defect exists in a valve or valve seat associated with a cylinder of a locomotive engine.